Key thing is to make sure the preamp is plugged correctly into the Octo sound card. The mechanical holes should line up perfectly. The 8 outputs are on the left side, the 6 inputs are on the right side.

There is no phantom power provided on the input side (some condenser microphones require phantom power).

NOTE: you can wire up without the preamp if you want to do field recording with only the 5V supply, however you will have to be careful and reduce the gains of the ADCs and DACs from full scale to get linear recordings without clipping.

For field recording, you can remove the preamp, however your dynamic range will be reduced.
In this case, the balanced breakouts can draw their power directly from the 5V output from the Pi's power supply. This means you only need to power the Pi and the balanced breakouts will be powered as well.

To use this setup, you will have to reduce your ADC and DAC gains from full scale to make sure you get a linear signal.